MT300/KH420碳纤维/聚酰亚胺树脂复合材料层合圆柱壳高温承载性能

基于Donnell-Mushtali近似理论及热弹性理论,考虑结构热变形和材料高温性能衰减等温度影响因素,对MT300/KH420碳纤维/聚酰亚胺树脂复合材料圆柱壳在常温、420℃及周向210~420℃不均匀温度场等热载工况下的承载性能进行了理论分析。并引入一阶屈曲模态缺陷作为几何初始扰动,利用ABAQUS,采用非线性显式动力学方法完成对MT300/KH420复合材料圆柱壳在以上热载工况下的轴压稳定性有限元仿真计算,计算结果与理论分析较为一致。设计并开展MT300/KH420复合材料圆柱壳力-热载荷联合轴压试验,获得圆柱壳在以上热载工况下的破坏载荷和破坏模式。研究表明:高温工况下,力学性能衰减和温场不均匀引起的结构热变形是影响MT300/KH420复合材料圆柱壳轴向失稳载荷的主要因素。      

模态缺陷条件下复合材料柱形壳屈曲特性

为了开展多模态缺陷条件下复合材料柱形壳的屈曲特性研究,进行了理想柱形壳在轴压工况下的线性屈曲分析,得出前50阶屈曲失稳模式,即模态缺陷;基于弧长法研究不同模态缺陷条件下复合材料柱形壳的非线性屈曲特性;将有限元分析结果、NASA SP-8007规范计算结果与Bisagni试验结果作对比分析。结果表明:对于轴压柱形壳屈曲问题,第1阶模态缺陷不是最差缺陷,在第1阶模态缺陷条件下求出的非线性屈曲载荷比试验值高出较多;高阶模态缺陷条件下的复合材料柱形壳非线性屈曲计算结果与试验结果最为吻合,两者相差较少;屈曲载荷下降受缺陷形状、幅值双重影响,复合材料柱形壳屈曲计算需考虑多模态问题;NASA求出的屈曲载荷非常保守,低于试验值较多,用NASA方法进行复合材料柱形壳的设计,往往会导致结构笨重、材料浪费、性能降低。     

纤维增强复合材料薄壁圆管扭转失效分析

对碳纤维增强树脂基复合材料（CFRP）薄壁圆管的扭转屈曲、失效载荷和失效模式进行了试验和数值模拟。试验观察圆管在扭矩作用下的3种失效模式,分析了不同失效模式的特征和机理。考虑圆柱壳的初始缺陷和非线性屈曲等因素,利用ABAQUS建立了圆管屈曲和损伤的有限元模型。结果表明:屈曲诱发圆管表面微裂纹的产生和扩展,对圆管的失效有着加速作用;扭转失效过程中圆管层间应力较低,层间分层主要由管壁突然的破坏产生;圆柱壳的初始缺陷对屈曲和失效载荷的模拟影响较大,本文通过对比计算结果和试验数据确定了圆管的初始缺陷系数;损伤模型的数值模拟结果与试验数据相一致,验证了有限元模型的有效性。      

加筋复合材料圆柱壳的屈曲和初始后屈曲的研究

本文分析了筋和壳的儿何参数及壳的铺层对纵向或环向密加筋的复合材料层合圆柱壳在轴压和侧压下的稳定性和初始后屈曲性能的影响。初始后屈曲分析基于Koiter理论。对几种不同几何参数、壳体铺层和载荷情况的加筋壳的计算表明:在所有情况下,外加筋比内加筋更有效地提高了屈曲载荷;复合材料壳的加筋效率一般都高于各向同性材料加筋壳;壳体的铺层对屈曲和初始后屈曲性能有很大影响。     

面芯脱粘缺陷对复合材料夹芯圆柱壳屈曲特性影响分析

面芯脱粘是复合材料夹芯结构常见的损伤形式。本工作综合考虑面芯界面损伤演化、分层屈曲以及分层扩展的耦合作用,建立了深水静压载荷下复合材料夹芯圆柱壳极限承载能力预报方法。基于非线性极限载荷计算方法,通过预制初始缺陷,开展了含面芯脱粘缺陷复合材料夹芯圆柱壳屈曲特性分析,揭示了典型面芯脱粘缺陷对复合材料夹芯圆柱壳失效模式及极限承载的影响机理,得到不同面芯脱粘形式、脱粘尺寸、脱粘位置的影响规律。研究发现,随贯穿面芯脱粘长度增加,结构失效模式发生整体屈曲→混合屈曲→局部屈曲演化;外蒙皮/芯层面芯脱粘对含环向贯穿面芯脱粘复合材料夹芯圆柱壳极限承载敏感度更高,内蒙皮/芯层界面脱粘对含纵向贯穿面芯脱粘缺陷复合材料夹芯圆柱壳极限承载敏感度更高;对于多个局部圆形面芯脱粘,沿纵向分布越集中、沿环向分布越离散,结构极限承载损失率越高。研究成果对面芯脱粘缺陷复合材料夹芯圆柱壳的优化设计与可靠性评估具有很好的指导意义。     

轴向冲击下复合材料圆柱壳的非对称动力屈曲

基于一阶剪切变形理论和非扁壳型几何方程，由Ｈａｍｉｌｔｏｎ原理导出包含初始几何缺陷的复合材料圆柱壳的非线性动力方程，Ｇａｌｅｒｋｉｎ方法得以位移形式表达的动力屈曲控制方程，通过有限差分方法求解，并由类似Ｂ－Ｒ准则方法判断动力屈曲是否发生；讨论了冲击速度，初始几何缺陷等因素对动力屈曲可能产生的影响。     

静水压下含缺陷中厚复合材料圆柱耐压壳的极限强度

为探究静水压下含缺陷中厚复合材料圆柱耐压壳的极限强度，以湿法缠绕工艺制备中厚玻璃纤维增强树脂基复合材料(GFRP)圆柱耐压壳结构模型，对其初挠度进行测试，并开展静水压破坏试验，分析了结构的极限承载能力、应变响应和破坏模式。基于实测初挠度及破坏模式，建立含缺陷复合材料圆柱壳的非线性分析有限元模型，同时考虑壳体几何缺陷及承压过程中的复合材料面内损伤，编制ABAQUS接口子程序USDFLD，对模型的损伤过程进行数值模拟，获得静水压下含缺陷中厚复合材料圆柱壳的渐进失效过程，并与试验结果对比验证。研究表明：在静水压下中厚GFRP圆柱壳结构在破坏前载荷几乎呈线性增加，最终破坏模式为材料的压缩破坏，整体屈曲破坏模式不明显。考虑结构的几何缺陷和材料损伤演化后，采用非线性有限元模拟得到的壳体极限强度与试验结果吻合良好，可以作为预测含缺陷中厚复合材料圆柱壳极限强度的方法。采用该方法对影响中厚复合材料圆柱耐压壳极限强度的关键参数进行了研究，为深海复合材料耐压壳的研究设计提供参考。     

圆柱壳限制失稳的实验研究

采用高分子高弹性材料Mylar薄膜制作衬壳,其外侧的刚性限制为钢制圆柱筒壳,两端用加强环压紧以模拟边界条件。用气压加载模拟圆柱壳受周向均匀压力,观察衬壳的屈曲过程,同时测量衬壳的临界载荷。实验测量结果与有限元计算的结果符合较好。另外还通过人为制造不同初始缺陷和变换不同壳体长度,研究了限制失稳临界载荷与初始缺陷及不同长度的关系。结果表明圆柱薄衬壳受侧向外压的限制失稳临界载荷比自由失稳临界载荷有很大提高。     

径向载荷作用下复合材料圆柱壳的非线性动力屈曲

采用半解析法求解径向阶跃载荷作用下复合材料圆柱壳的非线性动力屈曲。基于一阶剪切变形理论，由Hamilton原理推导出包含横向剪切变形以及几何初缺陷的圆柱壳的非线性动力方程，位移及载荷沿周向采用级数展开，由Galerkin方法得到微分方程组，通过有限差分法求解；根据响应情况，由B—R准则判定屈曲，确定屈曲临界载荷。     

受轴压黏弹性层合圆柱壳的极值点蠕变失稳

基于Donnell薄壳理论, 采用准弹性方法, 分析了含初始几何缺陷黏弹性层合圆柱壳极值点形式的延迟失稳特征。由轴向缩短量的突然增加定义失稳临界时间, 对玻璃纤维/环氧树脂层合圆柱壳进行了数值计算。结果表明: 圆柱壳存在临界时间趋于无穷的持久临界荷载; 表征延迟失稳程度的瞬时弹性临界荷载与持久临界荷载之差值随着初始几何缺陷的增加而减小; 边界条件、 铺设方式对延迟失稳的影响机制可通过对应弹性层合圆柱壳的缺陷敏感性分析来考察。      

Postbuckling of functionally graded fiber reinforced composite laminated cylindrical shells, Part I: Theory and solutions

Buckling and postbuckling behavior are presented for fiber reinforced composite (FRC) laminated cylindrical shells subjected to axial compression or a uniform external pressure in thermal environments. Two kinds of fiber reinforced composite laminated shells, namely, uniformly distributed (UD) and functionally graded (FG) reinforcements, are considered. The governing equations are based on a higher order shear deformation shell theory with von Kármán-type of kinematic non-linearity and including the extension-twist, extension-flexural and flexural-twist couplings. The thermal effects are also included, and the material properties of FRC laminated cylindrical shells are estimated through a micromechanical model and are assumed to be temperature dependent. The non-linear prebuckling deformations and the initial geometric imperfections of the shell are both taken into account. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths of FRC laminated cylindrical shells.     

Buckling of conical composite shells

A semi-analytical approach is proposed to obtain the linear buckling response of conical composite shells under axial compression load. A first order shear deformation shell theory along with linear strain-displacement relations is assumed. Using the principle of minimum total potential energy, the governing equilibrium equations are found and Ritz method is applied to solve them. Parametric study is performed by finding the effect of cone angle and fiber orientation on the critical buckling load of the conical composite shells.     

复合材料旋转壳稳定性有限元分析和横向剪切变形的影响分析

对复合材料旋转壳的失稳问题进行了有限元推导, 建立了考虑横向剪切变形的旋转壳稳定性分析模型。在应变向量阵中引入了横向剪切应变, 从而考虑了剪切的影响。为了避免剪切自锁, 刚度的计算采用一点高斯积分法, 几何刚度的推导采用Stricklin 法。最终将稳定性问题归结为特征值问题。数值算例表明, 对于各向同性和复合材料旋转壳, 横向剪切变形均使其临界载荷降低。在稳定性分析中, 横向剪切变形对各向同性材料旋转壳的影响较小, 对复合材料的影响较大。      

Progressive failure analysis for advanced grid stiffened composite plates/shells

A progressive failure methodology is developed to simulate the initiation and propagation of multi-failure modes for advanced grid stiffened (AGS) composite plates/shells on the basis of a stiffened element model. Failures of both skin and ribs are taken into consideration, which are matrix cracking, fiber failure, fiber–matrix shear failure, delamination in skin and fiber failure in rib. All these failures are defined using a set of 2-D stress-based polynomial failure criteria wherein the transverse shear stresses at centroid of the stiffened element are calculated by employing an integrated approach of finite element and finite difference method. Corresponding material and stiffness degradation behavior is introduced after the initiation of individual failure mechanisms. The progressive failure behavior of a composite orthotropic-grid curved panel with a centrally located cutout under compressive load is evaluated using the method.     

Dynamic buckling of metal matrix composite plates and shells under cylindrical bending

A micro-to-macro analysis is offered to investigate the dynamic response and buckling of metal matrix composite cylindrical shells and plates under cylindrical bending. The micromechanical analysis relies on the elastic fibers and inelastic matrix material properties, and provides the bulk behavior of the metal matrix composite at room and elevated temperatures. The macromechanical analysis employs the classical and higher order plate theories in conjunction with a spatial finite difference and temporal Runge-Kutta integrations to provide the dynamic response of the structure. The effects of the metallic matrix inelasticity, material rate sensitivity, shear deformation, fiber orientation, and initial geometrical imperfection on the behavior of the metal matrix composite structures are studied.     

纤维增强复合材料迭层圆柱壳的几何非线性分析

本文从非线性弹性理论出发,在小应变、中等小转动的前提下,全面考虑了变形对于平衡方程的影响,导出了和传统理论不同的壳体非线性理论;并用摄动法和伽略金法分别求解了四边不可动固支正交各向异性复合材料迭层园桂壳块以及考虑横向剪切的四边可动简支园桂形扁壳的非线性弯曲问题。计算表明:变形较大时,变形对所有平衡方程的影响都是值得注意的。      

Active damping of geometrically nonlinear vibrations of laminated composite shallow shells using vertically/obliquely reinforced 1-3 piezoelectric composites

This paper addresses the analysis of active constrained layer damping (ACLD) of geometrically nonlinear transient vibrations of laminated thin composite cylindrical shallow shells using vertically reinforced 1-3 piezoelectric composite (PZC). The constraining layer of the ACLD treatment is considered to be made of this 1-3 PZC material. The Golla–Hughes–McTavish (GHM) method has been implemented to model the constrained viscoelastic layer of the ACLD treatment in time domain. The Von Kármán type non-linear strain displacement relations and the first-order shear deformation theory (FSDT) are used for deriving this electromechanical coupled problem. A three dimensional finite element (FE) model of smart composite shallow shells integrated with a patch of such ACLD treatment has been developed to demonstrate the performance of the patch on enhancing the damping characteristics of thin laminated cylindrical shells, in controlling the geometrically nonlinear transient vibrations. The numerical results indicate that the ACLD patch significantly improves the damping characteristics of the shells for suppressing the geometrically nonlinear transient vibrations of the shells. The effect of variation of fiber orientation in the PZC material on the control authority of the ACLD patch has also been investigated.     

轴向冲击下环向加筋复合材料圆柱壳的非线性动力响应

采用半解析的方法，建立离散加筋圆柱壳模型，基于复合材料多层扁壳大挠度的剪切变形理论，利用Hamilton原理导出环向加筋复合材料圆柱壳的非线性运动控制方程；用Galerkin方法对空间变量进行离散，将位移和载荷展开为双级数，得到有关时间的常微分方程组，最后采用R-Kutta方法数值求解．通过算例，讨论了加筋肋骨几何参数、铺层角度、辅层方式、铺层层数等因素对动力响应的影响。     

Inter-laminar stresses in a laminated shallow shell panel

The evaluation of inter-laminar shear stresses in laminated shells using 2D finite element models involves cumbersome post-processing techniques. In this paper, a simple and efficient method has been proposed for accurate evaluation of transverse shear stresses in laminated composite shells by using a displacement-based C⁰ FE model derived from higher-order shear deformation theory (HSDT) and a least square error (LSE) method. In order to include the effect of three curvature terms in the strain components of composite shells, Sander’s approximations are followed. In this model, the first derivatives of transverse displacement have been treated as independent variables to overcome the problem of C¹ continuity in the FE implementation associated with the present shell theory (HSDT). The LSE method is applied at the post-processing stage, after in-plane stresses are calculated by using the present FE model based on HSDT. Thus, the proposed method is quite simple compared to the usual method of integrating the 3D equilibrium equations for the calculation of transverse stresses in laminated composite shells. The accuracy of the method is demonstrated in the numerical examples by comparison of the present results with those obtained from different models based on HSDT, exact analytical and 3D elasticity solutions.     

A co-rotational 8-node assumed strain shell element for postbuckling analysis of laminated composite plates and shells

 The formulation of a nonlinear composite shell element is presented for the solution of stability problems of composite plates and shells. The formulation of the geometrical stiffness presented here is exactly defined on the midsurface and is efficient for analyzing stability problems of thin and thick laminated plates and shells by incorporating bending moment and transverse shear resultant forces. The composite element is free of both membrane and shear locking behaviour by using the assumed natural strain method such that the element performs very well as thin shells. The transverse shear stiffness is defined by an equilibrium approach instead of using the shear correction factor. The proposed formulation is computationally efficient and the test results showed good agreement. In addition the effect of the viscoelastic material is investigated on the postbuckling behaviour of laminated composite shells. Received: 6 February 2002 / Accecpted: 6 January 2003 ID=" Present address: School of Civil Engineering, Asian Institute of Technology